Table 6.
Fitting data generated from mixture IRT to unidimensional 2PL IRT model: Condition 1 (Increase in item difficulty for Group 1 at Time 2).
| Item | Time 1 | Time 2 | Change | |||
|---|---|---|---|---|---|---|
| a1 | b1 | a2 | b2 | a1 − a2 | b1 − b2 | |
| 1 | 0.94 (0.07) | −0.69 (0.06) | 1.27 (0.08) | 0.06 (0.06) | −0.33 | −0.75 |
| 2 | 1.65 (0.10) | −1.38 (0.08) | 1.60 (0.10) | −0.38 (0.07) | 0.05 | −1.00 |
| 3 | 1.09 (0.07) | −0.71 (0.06) | 1.18 (0.08) | 0.05 (0.06) | −0.09 | −0.76 |
| 4 | 1.38 (0.08) | 0.44 (0.06) | 0.97 (0.07) | 1.13 (0.06) | 0.42 | −0.69 |
| 5 | 1.71 (0.10) | 0.88 (0.07) | 1.30 (0.09) | 1.65 (0.08) | 0.41 | −0.77 |
| 6 | 0.85 (0.07) | −0.68 (0.05) | 1.20 (0.08) | 0.03 (0.06) | −0.35 | −0.71 |
| 7 | 1.76 (0.11) | 1.93 (0.10) | 1.41 (0.12) | 2.81 (0.13) | 0.35 | −0.88 |
| 8 | 1.79 (0.11) | −0.81 (0.08) | 1.34 (0.08) | 0.11 (0.06) | 0.45 | −0.91 |
| 9 | 1.83 (0.14) | −2.59 (0.13) | 1.42 (0.10) | −1.49 (0.08) | 0.41 | −1.10 |
| 10 | 0.99 (0.07) | −1.12 (0.06) | 1.54 (0.09) | −0.27 (0.06) | −0.55 | −0.84 |
| 11 | 1.03 (0.07) | −0.60 (0.06) | 1.59 (0.10) | 0.24 (0.07) | −0.56 | −0.84 |
| 12 | 1.09 (0.08) | 1.37 (0.07) | 1.19 (0.09) | 2.16 (0.09) | −0.10 | −0.79 |
| 13 | 1.48 (0.09) | 0.54 (0.06) | 1.15 (0.08) | 1.30 (0.07) | 0.33 | −0.76 |
| 14 | 1.50 (0.09) | 0.13 (0.06) | 1.11 (0.08) | 0.91 (0.06) | 0.39 | −0.78 |
| 15 | 1.19 (0.07) | 0.04 (0.06) | 0.91 (0.07) | 0.69 (0.06) | 0.28 | −0.65 |
| 16 | 1.47 (0.10) | −1.50 (0.08) | 2.04 (0.12) | −0.49 (0.08) | −0.57 | −1.01 |
| 17 | 1.40 (0.10) | 2.19 (0.10) | 1.46 (0.13) | 3.11 (0.14) | −0.06 | −0.92 |
| 18 | 1.72 (0.11) | 2.09 (0.10) | 1.67 (0.14) | 3.13 (0.15) | 0.05 | −1.05 |
| 19 | 1.86 (0.11) | 1.06 (0.08) | 1.17 (0.09) | 1.83 (0.08) | 0.68 | −0.77 |
| 20 | 1.50 (0.09) | 1.12 (0.07) | 1.22 (0.09) | 1.88 (0.09) | 0.28 | −0.76 |
Simulated with 100 replications using posterior mode estimation. Values in parenthesis represent standard errors.